Internal reference voltage source equipped switching regulator



' Feb. '24, 197o DL'L. FRsoRlcKso-N ET AL. INTERNAL REFERENCE VOLTAGE some EQUIPPED SWITCHING REGULATOR (Filed A ril 5. 1967 I I v /0 71/ l2 REGULATED l4 VOLTA E vogsa SER'ES LE OUTPUT LOAD sou E SW'TCH FILTER SCHMITT l5 TRIGGER l6 FIG DC REFERENCE REGULATED H mm {/2 {/3 l4 VOLTAGE SOURCE PRIOR ART FIG 2 REGULATED INVENTORS DENNIS L. FREDRICKSON ALLYN L. GOTHE ATTORNEYS United States Patent Olfice 3,497,794 INTERNAL REFERENCE VOLTAGE SQURCE EQUIPPED WHTCH1NG REGULATOR Dennis L. Fredriclrson, Cedar Rapids, and Allyn L. Gothe,

Marion, Iowa, assignors to Collins Radio Company,

Cedar Rapids, Iowa, a corporation of Iowa Filed Apr. 5, 1967, Ser. No. 628,745 Int. Cl. GllSf 1/16 US. Cl. 32322 Claims ABSTRACT OF THE DISCLOSURE A switching DC voltage regulator having an internally developed reference voltage source with a Zener diode connected through a resistor to the input voltage source. This includes a connection across the Zener diode to a voltage divider having a tap connection as a highly accurate reference voltage source to the base of a transistor acting as a regulating voltage comparator with an emitter connection sensing the regulated output voltage. The collector of regulating voltage comparator transistor has a controlling voltage connection to the regulator switching voltage controlling Schmitt trigger circuit.

This invention relates in general to switching voltage regulators, and in particular to a switching voltage regulator having an internally developed highly accurate voltage reference, and developing a very high degree of output voltage regulation throughout an extended range of operational temperatures.

Various existing basic switching voltage regulators develop an output voltage filtered through a low pass LC filter, with the output voltage compared with a reference voltage for producing an error signal. In these basic switching voltage regulators using a trigger circuit, such as a Schmitt trigger, the resulting error signal derived from the output voltage and the reference voltage results in a series switch in the input voltage line being either open or closed thereby producing a series of voltage pulses that are integrated by the low pass filter in producing the desired output. In a basic switching voltage regulator the series switch would be, for example, a Darlington amplifier driven, or controlled, by a typical Schmitt trigger with the reference voltage compared with the output voltage being the voltage developed across a Zener diode, and with the resulting voltage being used for controlling the state of the Schmitt trigger. With a Zener diode being used in this manner for establishing a reference, in such a switching voltage regulator designed for providing a five volt output, the output generally will not meet the tolerance limitation requirements of 10.25 volt DC throughout the range of operational temperature variation, for example, 30 C. to +80 C. Much of the difliculty arises since Zener diodes below about six volts cannot be temperature compensated and also because they have typically soft knee characteristics. Furthermore, tolerances of the Zener developed voltage itself is such a variable as to significantly contribute to the problems encountered with such basic switching voltage regulator circuits.

It is, therefore, a principal object of this invention to provide a switching voltage regulator capable of meeting intensified DC voltage output regulation tolerance limitations throughout an extended operational environmental range of temperature.

Another object is to provide such a switching voltage regulator with a Zener diode used in a voltage divider being biased by the input voltage well beyond the area of soft knee characteristics.

Features of this invention useful in accomplishing the above objects include, in a switching voltage regulator 3,497,794 Patented Feb. 24, 1970 developing a very high degree of output voltage regulation throughout an extended range of operational temperatures, a Zener diode connected through a resistor to the input voltage source actually a variable level DC voltage supply, and a connection across the Zener diode to a voltage divider with the Zener biased beyond the knee characteristics area of operation throughout wide voltage swings of the DC voltage supply. The voltage output sensing device in this instance is a transistor with the emitter connected through a resistor to the output voltage line of the regulator and the base connected to a tap of a voltage divider having a relatively stable voltage applied thereto as developed by the Zener diode, and the collector of the transistor has a controlling voltage connection to the regulator switching voltage controlling Schmitt trigger circuit. The voltage divider involved also includes a diode so subject to characteristic variation change with temperature variation as to compensate changes in emitter to base impedance of the output voltage sensing transistor with variation in environmental temperature.

Specific embodiments representing what are presently regarded as the best modes of carrying out the invention are illustrated in the accompanying drawing.

In the drawing:

FIGURE 1 represents a block diagram of a basic switching regulator;

FIGURE 2 is a schematic showing of a prior art switching regulator conforming to the block diagram of FIG- URE l; and

FIGURE 3, a schematic of applicants improved highly eificient switching voltage regulator with intensified DC voltage output regulation tolerance limitations throughout an extended operational environmental range of temperature.

Referring to the drawing:

With the block diagram showing of FIGURE 1 of a basic switching voltage regulator 10', a DC voltage source 11, subject to a relatively high degree of DC voltage variation with loading, or from other effects, of from 20 to 30 volts, supplies a voltage input to series switch circuit 12 with an output passed as an input to low pass LC filter circuit 13. The output of the low pass filter 13 is passed as a regulated voltage to a load 14. The output of low pass filter 13 is also connected to a voltage mixing or comparing circuit 15 that is also connected to DC reference voltage source 16. The resulting voltage output of voltage mixing or comparing circuit 15 is connected as the controlling voltage input to a Schmitt trigger circuit 17 the output of which is applied as a control for the series switching circuit 12.

In the prior art basic switching regulator 10 of FIG- URE 2' the relatively highly variable DC voltage supply 11 has a number of output circuit connections, with its connection to the series switch circuit 12, including a connection through capacitor 18 to ground, a connection through series connected resistors 19 and 20 to the common junction of the collector of trigger circuit NPN transistor 21 and the base of NPN transistor 22 of Schmitt trigger circuit 17. Please note that the common junction of the series connected resistors 19 and 20 is connected to the cathode of Zener diode 23 the anode of which is connected to ground in order to establish a relatively stable reference voltage for the collector to base connection of transistors 21 and 22 in the Schmitt trigger circuit 17. The voltage input line from DC voltage source 11 is also connected through a combination bias and Schmitt trigger output signal interconnecting circuit with the series switch 12 including a resistor 24 connected at one end to the input DC voltage line and at the other end to resistor 25, capacitor 26 and the base of PNP transistor 27 of the series switch circuit 12. The other end of resistor 25 and the other side of the capacitor 26 are connected in common to the collector of NPN transistor 22 of the Schmitt trigger circuit 17. The emitters of transistors 21 and 22 of the Schmitt trigger circuit 17 are connected in common through resistor 28 to ground. Referring back to the series switch circuit 12, the emitter of PNP transistor 27 is connected to the DC voltage source input line, and the collector is connected both to the base of NPN transislor 29, the collector of which is connected to the DC voltage input line, and through resistor 30 to the output line of the series switch 12 connected to the emitter of the series switch circuit 12 transistor 29. This output line is connected to the low pass LC filter circuit 13 and includes a connection to the cathode of diode 31 the anode of which is connected to ground, and then it is connected to and through coil 32 and on the output side of coil 32 through capacitor 33 to ground.

The output connection regulated voltage line extending from the common junction of coil 32 and capacitor 33, of the low pass filter 13, extending to load 14 is connected to the cathode of Zener diode 34, and serially on through resistor 35 as part of the voltage comparing circuit 15 in the circuit of FIGURE 2. In this prior-art circuit the ground connection of resistor 35 is the DC voltage ref erence 16 of FIGURE 1. The common junction of the anode of Zener diode 34 and resistor 35 is connected as the trigger circuit controlling voltage input to the base of NPN transistor 21 of Schmitt trigger circuit 17.

Referring now to the applicants improved relatively low voltage switching regulator of FIGURE 3 components and subcircuits duplicating those of the prior art basic switching regulator of FIGURE 2 are numbered the same as a matter of convenience, and those circuits that are changed are given corresponding primed numbers and new and/ or ditferent components are given new numbers. Improvements with this low voltage switching regulator 10" include a line extension from the common junction of the cathode of Zener diode 23 and resistors 19 and 20 to the anode of diode 36 and connection serially on through adjustably tapped resistor 37 and resistor 38 to ground. The adjustable tap 39 of resistor 37 is connected through resistor 40 to the base of PNP transistor 41. The emitter of PNP transistor 41 is connected through resistor 42 to the regulated voltage output line from the common junction of coil 32 and capacitor 33 of low pass filter 13. The collector of PNP transistor 41 is connected through resistor 43 to ground and also as a trigger circuit controlling voltage source input to the base of NPN transistor 21 of the Schmitt trigger circuit 17. This provides control circuitry in a switching regulator developing a relatively low regulated voltage output with greatly improved regulation tolerances throughout an extended operational environmental range of temperatures. A relatively stable ref erence voltage is developed at the cathode of the Zener diode 23 connected through a resistor circuit to the input voltage source since the Zener diode 23 is a low current Zener operated beyond the knee characteristics area of operation throughout the normally experienced wide voltage swings of the DC voltage supply 11. The Zener developed voltage is used as the voltage impressed through diode 36 upon a voltage divider and with the voltage divider having a tap providing a relatively stable DC voltage reference source 16 connection to the base of a transistor in the mixing or comparing circuit The emitter of this sensing or voltage mixing circuit 15 transistor is connected to the regulated voltage output line with the transistor being activated by variations of voltage between the output line as determined by the voltage bias and current flow between the emitter and base of the transistor 41 for developing control voltage outputs at the collector of the transistor.

Please note that the improved control circuitry of the relatively low voltage switching regulator of FIGURE 3 provides particularly advantageously improved operation where regulated voltage output is so low as to not bias a Zener diode, onnected, as with the rior art regulator of FIGURE 2, directly to the regulated voltage output line, beyond the knee characteristics area of operation. This would be true, for example, in a specific case where the desired regulated voltage output called for is 5 volts:0.25 volt throughout a 3'0 C. to C. range, actually a :01 tolerance limitation. With, for example, a 1N4099 Zener diode this voltage level is right in the knee characteristic area of operation or below to thereby present unsatisfactory operational results with circuitry such as the prior art circuit of FIGURE 2. The Zener diode 23, however, with its connection through resistor 19 to the DC voltage supply 11 that is variable over a rather extended DC range of from 20 volts to 30 volts develops a relatively stable 6.8 volts at the cathode since it is being operated beyond the knee characteristics area of operation.

Components used in applicants internal reference voltage source equipped relatively low voltage output switching regulator, as shown in FIGURE 3, with a DC voltage supply input ranging from 20 to 30 volts that has provided a regulated voltage output well within the requirements of 5 voltsi0.25 volt over a 30 C. to +80 C. range with the output having varied only from 4.93 volts to 5.03 volts over the temperature range, include the following:

2N706 1N4099 1.5K 22K 0.001 2N2907 Whereas this invention is here illustrated and described with respect to a single embodiment thereof, it should be realized that various changes may be made Without departing from the essential contributions to the art made by the teachings hereof.

We claim:

1. .In a switching voltage regulator, input connection means for connection to a DC voltage supply generally subject to a relatively high voltage swing as compared to DC voltage output regulation tolerance requirements throughout an operational range of environmental temperature; series switch means receiving an input through said input connection means and developing an output; low pass filter means connected for receiving the output of said series switch means and smoothing the signal passed as a regulated DC voltage output; trigger circuit means connected for controlling said series switch means; a voltage comparing circuit connected to sense the regulated DC voltage output of said low pass filter means and to said trigger circuit means as the controlling voltage input source for said trigger circuit means; and a Zener diode with a first electrode connected to a voltage potential reference source, and with a second electrode circuit connected through impedance means to said input connection means, and also circuit connected to said voltage comparing circuit for providing a reference voltage compared to the regulated DC voltage output for regulating control of the switching voltage regulator.

2. The switching voltage regulator of claim 1, wherein the first electrode of said Zener diode is the anode of the Zener diode and the voltage potential reference is ground; and the second electrode of the Zener diode is the cathode of the Zener diode.

3. The switching voltage regulator of claim 1, wherein said voltage comparing circuit includes a multielectrode solid state device with a first electrode connected to sense the regulated DC voltage output of said low pass filter means, a second electrode connected to said Zener diode for a reference voltage connection, and a third electrode connected to said trigger circuit as the controlling voltage input source connection for said trigger circuit means.

4. The switching voltage regulator of claim 3, wherein the circuit connection between the Zener diode and said voltage comparing circuit includes a voltage divider.

5. The switching voltage regulator of claim 4, wherein a solid state diode is included in the circuit connection between the Zener diode and said voltage comparing circuit.

6. The switching voltage regulator of claim 5, wherein the voltage divider includes a tapped resistor, and with the connection from the Zener diode being to and through said solid state diode to one end of said tapped resistor; the other end of said tapped resistor being connected to a voltage potential reference source; and the tap of said tapped resistor being connected to the second electrode of said multielectrode solid state device.

7. The switching voltage regulator of claim 6, wherein said multi-electrode solid state device is a transistor with said first electrode an emitter, the second electrode the base, and the third electrode the collector of the transistor. x i

8. The switching voltage regulator of claim 7, wherein said transistor is a PNP transistor with the collector connected to ground through a resistor, and from the junction of the collector and the resistor to said trigger circuit.

9. The switching voltage regulator of claim 8, wherein the regulated voltage output is a positive voltage; said trigger circuit is a Schmitt trigger circuit including two transistors; and with the connection from the collector of the transistor of the voltage comparing circuit to the trigger circuit being to the base of one of the transistors of the Schmitt trigger circuit.

10. The switching voltage regulator of claim 7, wherein said Zener diode is a relatively low current diode operated beyond the knee characteristics area of operation, and develops a voltage reference at said second electrode having a greater absolute value than the absolute value of the regulated voltage output of the regulator.

References Cited UNITED STATES PATENTS 2,776,382 1/1957 Jensen. 3,086,163 4/ 1963 Francois. 3,102,225 8/1963 Kenny et al. 3,350,628 10/1967 Gallaher et al. 3,403,321 9/ 1968 Mosak.

LEE T. HIX, Primary Examiner A. D. PELLINEN, Assistant Examiner 

